Nitriding ferrous alloys



2 5 sociatin 'v certain specially 35 conform. to

Patented Apr. 18, 1933 UNIT D STATES PATENT-OFFICE j aon n a. EGANI, or BROOKLYN. NEW YORK, AssrGnoR 'ro ELEGTRQ METALLURGICAL r COMPANY, A conromrrron or cwnsrvrnemm NITRIDING FEBROUS ALLOYS No Drawing.

My invention relates to the production. of 'nitrided layers or cases on ferrous materials by heating the materials in gaseous nitrogen-containing substances and especially to 5 the production of hard, wear-resistant cases. The object of my invention is to provide means for accelerating and intensifying the action of nitriding gases on ferrousmaterials so as to reduce the time required to produce a case of given hardness or thickness.

It is advantageous to produce the cases referred to by heating the objects to be cased for about 12 to hours in the presence of ammonia at temperatures below'the-ni- 15 tride eutectoid temperature of the steel. Ac-

cordingly, low temperatures, such'as about 460 C.'to580 C. have been generally used. To produce these hard nitrogen-containing cases at low temperatures, at least a critical 2o amount of an alloy promotlngagent, such as aluminum or vanadium is contained in the alloy upon which the case is to be produced.

"I have found that the action of gaseous nitriding agents is intensified by closely asg pre-nitrided alloy material with the surface tobe hardened. The material is referred to herein asaccelerator. Any form of the material may be used which will readily conform tothe parts to be hardened and provide pores so as to al- "low access of the gas to the surface to be hardened. For example, metal in a, state of subdivision, such as filings, powder, wire or 'wire gauze which can readily; be made to the surface of the objector presen many'pomts of contact therewith are preferred but other forms may be used. The accelerator comprises a ferrous alloy containing at least one nitride promot- 40 ing agent. For example a pre-nitrided ferrous alloy containing aluminum acts energetically as an'accelerator for nitriding alloy' steels which contain aluminum as the promoting agent. However, more than one agent maybe present in the accelerator. For example, vanadium may he present in an aluminum containing accelerator, in which case the material is suitable as nitride promoting an accelerator for nitriding alloys containing either or both aluminum or Application filed March 14, 1930. Serial No. 435,971.

vanadium as the promoting agent. In like manner, vpre-nitrided ferrous alloys containing other nitride promoting agents act as accelerators. Thefbest results have been obtained by using accelerators composed of alloys which contain the same nitride promoting agents as the alloys to be nitrided, but it is not always necessary that the same promoting agent shall be present in both the accelerator and the alloy to be nitrided. The accelerator may be pre-nitrided. by heating to critical temperatures in the presence of any nitriding agent, such as ammonia. In general, the critical temperature range is the same as that which maybe used to produce hard, wear-resistant coatings on ferrous alloys containing nitride promoting alloy agents,the maximum temperature being known as the nitride eutectoid temperature. The maximum temperature 'of this range is about 580 C. and'the minimum temperature is limited by the time of treatment and the atomic mobility of the reacting substances, approximately 400 C. being the practicable lower limit. Accelerating material which is pre nitri-ded at temperatures below the nitride eutectoid temperature may be used repeatedly. The acceleration produced by .prenitrided material decreases as thetemperature used for pre-nitriding isincreased above the nitride eutectoid temperature. The nitrideeutectoid temperature for the alloy of the accelerator isabout the practicable maximum pre-nitriding temperature.

As illustrative ofmy invention,steel alloy filings composed of steel containing about 1% aluminum as a promoting agent were pre-nitridedby heating them at about 460 G. in an atmosphere of ammonia for12'to 16 hours. A steel alloy article composed of steel containing about 1% aluminum-as a promoting agent was embedded in the .prenitrided steel filings in a closed container. The air in the container was displaced with ammonia and the contents were heated to 460 C. for 4 hours. The article'was found to have a thin,'hard, wear-resistant coatlng equal in hardness t'o thecoatingsproduced V by treating like articles for 16'hours at the .at least one nitride promoting perature thereof.

same temperature but without the use of the pre-nitrided alloy filings.

A second alloy article of the same composition was embedded in filings of the same alloy which had not been pre-nitrided. The article was heated .to 460 C. for 4 hours in the presence of ammonia but no appreciable hardening of the surface of the article was produced.

A third article of thesame composition was embedded in similar alloy filings which had been pre-nitrided at 700 0., a temperature higher than the nitride eutectoid temperature. No appreciable surface hardness was produced by heating in ammonia for 1 hours. Y

Instead of'usingthe above described prenitrided material alone, it may be used in conjunction with inert substances and with other accelerators. Owing to the wide range of modification of which the invention is capable, applicant does not wish to be understood as limiting the invention to the modifications specifically described except as limitations are imposed by the prior art or as indicated inthe appended claims.

I claim:

1. A nitriding accelerator comprising metallicsubdivided material, said material eing composed of ferrous alloy containing agent and a nitrogenous substance of the same kind that is produced by nitriding a steel which contains at least one nitriding promoting agent, said accelerator being prenitrided at temperatures below the nitride eutectoid tem- 2. Method of accelerating the production of-nitrided cases by the action of nitriding gases which comprises closely associating with the surface to be hardened pre-nitrided ferrous alloy containing atleast one nitride promoting a ent.

3. The method of producing a nitrided case on a ferrous alloy object containing a nitride promoting agent which comprises closely associating with the object a subdivided material comprising a pre-nitrided ferrous alloy containing at least one nitridepromoting agent, and heating ing a ent.

4. he method of producing a nitrided case on a ferrous allov object containing anitride promoting agent which comprises closely associating with the object a subdivided material comprising a pre-nitrided ferrous alloy containing at least one of the same nitride promoting agents as the object, and heating in the presence of a nitriding agent.

5. The method of producing a nitrided case on a ferrous alloy obiect containing a nitride promoting agent which comprises placing in in the presence of a nitridcontact with the object, a subdivided material comprising a pre-nitrided ferrous alloy containing the same nitride promoting agent a ferrous as the object, and heating in the presence of a nitriding agent.

6. The method of producing a hard "nitrided case on a ferrous alloy object containing sufficient of a nitride promoting agent to produce a hard, adherent coating by heating in the presence of ammonia which comprises closely associating the object with a subdivided material comprising a pre-nitrided ferrous alloy containing one of-the same nitridepromotingagents as the object, and heating in the presence of a nitriding agent to temperatures of about 460 C. to 580 C.

7. A nitridi-ngaccelerator comprising nitrided metallic subdivided material which contains at least one nitride promoting agent of the group comprisingaluminum and vanadium. I

8. A nitriding accelerator comprising ferrous subdivided material which contains at least one nitride promoting agent of the group comprising aluminum and vanadium, said material being prenitrided at temperatures below the nitride eutectoid temperature thereof.

9. Method of accelerating the production of nitrided cases on ferrous materials, by the action of nitriding gases which comprises closely associating with the surface to be hardened prenitrided ferrous subdivided material containing at least one nitride promoting agent of the group consisting of aluminum and vanadium.

10. Method of-accelerating'the production of nitrided cases on aluminum-containing ferrous materials by the action of ammonia at nitriding temperatures below about 580C. which comprises closely associatingwith the surface-to be hardened prenitrided steel alloycontaining aluminum, prenitrided at temperatures below the nitride eutectoid temperature thereof.

11. Method of accelerating the production of nitrided cases on vanadium-containing ferrous materials by'the action. ofammonia at nitriding temperatures below about 580 C. which comprises closely'associating with the surface alloy containing vanadium, said .alloy being prenitrided at temperatures below the nitride eutectoid temperature thereof.

12. Method of producing a nit-rided case on alloy obiect. which comprises closely associating'with the object a subdivided material comprising prenitrided ferrous material which contains at least one nitride promoting agent chosen from the group consisting of aluminum andvanadiuim-and heating at temperatures below about 580 C. in -the presence of ammonia.

In testimony whereof, I aflix my signature.

JOHN/J. EGAN.

to be hardened prenitrided steel 

